Mixers and samplers can be found in most high frequency communication systems. For example, mixers are commonly used to shift signals from one frequency range to another for convenience or compatibility in transmission or signal processing. Samplers, on the other hand, are generally used to convert continuous signals into discrete signals for signal processing.
The performance of a mixer or sampler can be evaluated according to parameters such as bandwidth, noise, and gain, among others. As information rates go up, the bandwidths of the underlying components like mixers and samplers must also increase. Similarly, adequate noise and/or gain values are required to maintain quality of the processed information. Each of these parameters is important for most modern systems, as developers are continually pushing the envelope of processing speed and quality.
In high frequency mixers and samplers, bandwidth, noise and gain are sensitive to intrinsic device characteristics and parasitics. In addition there are tradeoffs to be made between these parameters. It is difficult in general to improve one without sacrificing the other two. One technique for optimizing these parameters is by distributing the devices along a transmission line. A basic implementation of this technique can be found in a travelling wave amplifier.
In addition as a consequence of this strong sensitivity to device parasitics, high frequency mixers and samplers are commonly implemented with specialized devices or processes that minimize or reduce parasitics. For example, some mixers or samplers may be implemented with pseudomorphic high electron mobility transistors (pHEMT), which tend to have relatively low parasitic C. Similarly, some mixers may be manufactured by forming a mixer bridge with specialized processes typically used to manufacture tow capacitance diodes.
Unfortunately, these specialized devices and processes are generally expensive and inefficient to manufacture. Consequently, there is a general need for improved designs for high performance mixers and samplers.